Method of slime beneficiation



United States Patent 3,259,326 METHOD OF SLIME EENEFICIATION James B. Duke, Metuchen, and Ernest W. Greene, Westfield, N.J., assignors to Minerals & Chemicals Philipp Corporation, Woodbridge Township, N.J., a corporation of Maryland No Drawing. Filed Feb. 15, 1965, Ser. No. 432,843 7 Claims. (Cl. 2411-20) This application is a continuation-in-part of our copending application, Serial No. 197,605, now abandoned, filed May 25, 1962.

This invention relates to the flotation of very finely divided or slimed ores and is directed, especially, to the selective froth flotation of slimed ores which are normally not especially responsive to beneficiation by flotation.

An object of this invention is the provision of a method for creating new surfaces on slimed mineral particles, thereby improving the response of the particles to selective concentration, as by froth flotation.

A specific object of this invention is the provision of a method for creating new surfaces of mineral particles that are so fine as to be classified as colloidal.

A specific obiect is an attrition treatment of an extremely finely divided ore pulp, such as aqueous phosphatic slimes, before flotation treatment in the presence of an added collector reagent, to improve the response of the ore pulp to the subsequent flotation treatment.

Ores are usually ground before froth flotation treatment in order to liberate mineral values since one mineral species must be liberated from a second mineral species in order to float selectively one species from the other. Still another reason for grinding ores before froth flotation is to produce or create new surfaces on mineral particles. This may be done before the ore pulp is treated with collector reagents and before the flotation concentration step or steps. The reason for creating the new surfaces is that in numerous cases minerals with new surfaces are appreciably more responsive than minerals with aged surfaces to selective flotation concentration in the presence of added collector reagents. Thus, certain ores must be freshly ground a short time before flotation in order to realize adequate selective flotation concentration. To create the desired new surfaces on mineral particles, the ores can be wet ground in a ball mill, tube mill, pebble mill, etc. Irrespective of the grinding method that is used, the grinding is usually controlled to minimize the formation of slimes, especially so-called colloidal slimes, which are slimes containing a substantial quantity of particles finer than 10 microns, equivalent spherical diameter. Another method for creating new surfaces, as practiced by the industry, is by attrition mixing in which a concentrated ore pulp is attrited by mixer blades or propellor blades during the conditioning step. In this case, the desired new surfaces may result from the removal of an adherent slime coating on the mineral particles.

Prior to the subject invention, it was not possible to create new surfaces on slimed minerals, especially colloidal slimes, since the grinding equipment and attrition mixers used with ores to liberate mineral values and/ or to create new surfaces, are ineffective in grinding material in the minus 10 micron size range. Moreover, prior to our discovery and invention, it wouldhave been considered undesirable to grind or attri-te slimes. The prior art, virtually Without exception, teaches that slimed ores, especially ores composed of colloidal slimes, are too fine to respond to conventional selective froth flotation. In fact, the prior art emphasizes the fact that slimes have an adverse effect on the froth flotation of most ores and ores are almost invariably deslimed before froth flotation.

3,259,326 Fatented July 5, 1966 We have discovered a simple and highly effective method for renewing the surfaces of slimed minerals and have further discovered that slimed minerals, thus treated, are more responsive to froth flotation.

Stated briefly, in accordance with this invention a substantial quantity of plus 325 mesh, preferably minus 10 plus 35 mesh, particles of a hard inert grinding medium, such as sand or steel shot or grit, is incorporated into a minus 325 mesh slimed aqueous ore pulp containing a substantial quantity of minus 10 micron particles. The abrasive particles are inert with respect to the constituents of the ore. The slimed pulp with added abrasive particles is then tumbled, preferably in a partially filled horizontal cylinder or drum. The drum with contents is continuously rotated about its horizontal axis at a speed such that the pulp with added abrasive particles is substantially in the form of an integral body or a pool adjacent the lower portion of the drum, with the abrasive particles being suspended within the pulp and the individual particles continuously traveling in closed, generally elliptical paths largely within the pulp. In other words, little splashing occurs and the pulp and abrasive particles do not rotate in a circular path within the drum. The drum with contents is rotated until the desired extent of resurfacing takes place. Frequently resurfacing results in appreciable apparent particle size reduction, as determined by a sedimentation procedure described hereinafter. After the treatment of the pulp with the finely divided abrasive particles, the abrasive particles are separated from the pulp by decantation or screening and the pulp is then subjected to froth flotation.

Our invention will be more fully understood by the following description of its application to the beneficiation of phosphatic slimes.

Slimed phosphatic ores obtained by washing of phosphate-bearing matrix, as described hereinabove, have an appreciable phosphate content. Typically they analyze about 20% to 35% *BPL (bone phosphate of lime or Considerable thought has been given in the past to the problem of recovering at least some of the phosphate values in phosphatic slimes. In fact, of such national interest is the problem of handling phosphatic slimes that the problem was extensively taken up by a government and industry panel which reported its findings and recommendations in a publication by P. M. Tyler and W. H. Waggmen, entitled Report on Possible Utilization of Phosphate Rock Slimes, published by the National Academy of Sciences, National Research Council, June 29, 1953. Froth flotation was one of the many possible beneficiation process which was considered by the panel and reported upon in the aforementioned publication of the National Academy of Sciences. However, it was recognized that slimed phosphatic ore, as other extremely finely divided materials containing colloidal particles, are not considered to be amenable to usual froth flotation techniques and, in fact, impair phosphate flotation when present in the flotation feed. Therefore, the concentration of phosphate values in the slimes was considered to be a doubtful prospect without at least initial selective flocculation of the colloids in the slimes or without the development of highly specialized reagents and/or preconcentration techniques.

In accordance with this invention, an excellent recovcry of a phosphatic concentrate of commercially valuable BPL grade is produced from aqueous phosphatic rock slimes by the following essential steps:

(1) Minus 325 mesh slimes obtained by hydraulic washing of phosphate rock are preconditioned for froth flotation by agitating the aqueous slimes with particles of a hard inert plus 325 mesh grinding medium such as,

for example, sand, and separating said grinding medium from the slimes.

(2) The aqueous ground slimes, preferably after being treated with a deflocculating agent, simultaneously with or subsequent to agitation with the particles of grinding medium, are then conditioned for froth flotation by agitating the slimes with an alkali, a higher fatty acid collector reagent, a hydrocarbon oil reagent, and, optionally, an oil-soluble, water-insoluble petroleum sulfonate.

(3) The slimes thus conditioned are subjected to froth flotation in an alkaline circuit thereby producing a froth product which is a concentrate of phosphate values in the slimes (principally in the form of apatite) and a tailing product which is a concentrate of aluminum and iron values, together with a clayey material and other impurities originally in the slimes. Normally, the froth product is cleaned several times by being subjected to further froth flotation to improve upon the grade of the phosphate enriched material. The phosphate recovery may be further improved by recirculating middling material from previous flotation residues.

By agitating the aqueous slimes with grinding medium before conditioning the slimes with phosphate collector reagents, in accordance with our invention, a spectacular improvement in concentration grade can be achieved without significant reduction in recovery. This result can be obtained with a modest degree of particle size reduction and is not significantly improved by prolonged agitation of the slime with grinding medium which would effect a further increase in particle size reduction. The combined grinding and froth flotation can lead to the production of commercially useful concentrates from slimed feed which afford concentrates of very limited commercial utility in the absence of the preliminary grinding treatment. Thus the process of this invention has resulted in the recovery from waste slimes of concentrates which possess a satisfactory BPL grade for furnace feed as well as for use in fertilizer manufacture.

Phosphate rock slimes amenable to the process of this invention are obtained by hydraulic washing of the ore either during hydraulic mining of the ore or by a separate hydraulic classification of the ore which has been dry mined. During the hydraulic washing, fine sizes of mineral materials remain suspended in the water. The aqueous suspension or slime is then removed from the sediment which is beneficiated by means known to those skilled in the art. Normally, essentially all of the solids in slimes which are the tailings produced by a hydraulic washing of phosphate matrix are finer than 400 mesh (Tyler) and comprise for the most part argill-aceous minerals (principally apatite). In most instances, the slimes will contain no more than about 2% to 3% by weight of particles coarser than 325 mesh (Tyler). Of the minus 325 material an appreciable portion is colloidal. The particle size distribution of the slimes will vary with the origin of the slimes, Western phosphate rock slimes, for example, being somewhat coarser than Florida slimes or Tennessee slimes. By way of illustration, a typical particle size distribution curve of Florida slimes indicates an average equivalent spherical diameter (E.S.D.) of less than about 0.1 micron, as compared with an average E.S.D. of about 0.3 micron for Tennessee slimes and about 5 microns for Montana slimes.

It is also within the scope of this invention to employ phosphatic (or other) slimes which have been obtained by a hydraulic washing in which an alkaline deflocculating agent is contained in the wash water for the purpose of controlling the washing operation to produce the desired solids content in the slimes. As examples of suitable deflocculating agents may be mentioned sodium silicate, ammonium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate and mixtures of sodium silicate with one or more of the aforementioned alkaline hydroxides. In present practice where deflocculating of the system at about 6% to agents are not added in the washing operation, effluent slime solids in the overflow may be about 4% or lower. Such slimes then would require a subsequent thickening operation to obtain the desired solids for flotation. By employing the deflocculating agent in the wash liquid, slimes at solids contents considerably higher than 4% can be produced directly.

Silica sand has been used with good results as the grinding or polishing medium although other inert attrition-resistant particles such as zircon sand or even metal particles of the same or different particle size can be used. The use of steel grit or shot, especially minus 10 plus 35 mesh shot or grit, is recommended. Total solids (slimes plus grinding particles) of the slip during agitation can be about 70% to with the slime solids The slimes should be distinctly fluid when agitated with grinding medium. The deflocculating agent can be incorporated into the slimes before the slimes are agitated with the grinding medium to permit operation at higher slime solids. The rotation of the slimes with grinding medium can be carried out for a time within the range of a few minutes to about 20 hours, usually at least 10 minutes, to obtain significant benefits. Rotation of the slimes and grinding medium for short periods will suffice when mere polishing of the solids in the slimes is desired. Prolonged rotation will result in substantial particle size reduction of the slimed solids which may produce superior results in some instances. The particle size reduction of the slimed solids brought about by agitating the aqueous slimes with grinding medium need not be spectacular and, surprisingly, the response of the Wet ground feed to flotation is apparently not affected one way or another by prolonged grinding. By Way of example, it was found that, with a phosphatic slime having an average E.S.D. of 5.5 microns, sand grinding to an E.S.D. of about 1.5 microns was as effective in conditioning the slimes for flotation as grinding to an E.S.D. of 0.8 micron. In fact, polishing with a modest size reduction may be as suitable as true grinding with a major reduction of particle size. The optimum particle size of the ground or polished slime will vary with the particle size of the starting slimes and, generally speaking, the ground slimes will be considerably more responsive to phosphate flotation than unground slimes of substantially the same equivalent spherical diameter. After agitation of the slimes with the grinding medium is completed, the slimes are separated from the grinding medium, as by decantation or screening.

If the slimes have not been deflocculated at a previous point in the process, the deflocculating agent can be incorporated with agitation into the aqueous slimes after they are separated from the grinding medium.

The quantity of deflocculating agent employed does not appear to be critical and, to achieve the full benefits of its use, this reagent should be employed in amount suflicient to deflocculate the dilute slimes, as evidenced by a marked thinning of the slimes.

The pH of the deflocculated slimes is on the alkaline side, a pH within the range of about 7.5 to 9 being suitable.

The previously ground aqueous phosphatic slimes are then conditioned in any suitable agitated vessel with a carboxylic negative-ion collector reagent and cooperative reagents, preferably in the form of an emulsified mixture. As examples of suitable negative-ion reagents may be mentioned higher fatty acids, such as fish oil fatty acids, oleic acid, resin acids, mixtures of higher fatty acids with resin acids (e.g., tall oil acids), soaps of the aforementioned, wood by-product fatty acids, higher sulfo-fatty acids, and salts of the aforementioned. The cooperative reagent is a neutral hydrocarbon oil such as fuel oil, kerosene, mineral oil, gasoline ,or diesel oil. An oil-soluble, water-insoluble petroleum sulfonate reagent can also be employed. Oil-soluble, water-insoluble petroleum sulfonates are prepared by sulfonation of suitable petroleum fractions with concentrated or fuming sulfuric acid and are commercially available in the form of solutions of the sodium, calcium, barium or ammonium salts in about an equal weight of mineral oil. These solutions may be used as the sole cooperative reagent or a mixture of the solution with additional neutral oil may be used. The oilsoluble petroleum sulfonates have a higher molecular weight than water-soluble petroleum sulfonates. Usually, the molecular weight of an oil-soluble petroleum sulfonate is at least 400.

During conditioning, the pH of the phosphatic pulp should be adjusted to the 8.0 to 9.5 level when necessary by addition of sodium hydroxide or ammonium hydrox ide.

The conditioned phosphatic pulp is subjected to aeration in any suitable cell, producing an apatite rich froth and a tailing. As in other flotation processes, product grade and efficiency of concentration will be improved by refloating the froth product. In this particular flotation process there should be an advantage in recirculating middling material from previous flotation residues.

Following are examples which illustrate the exceptional grade and recovery of phosphate values that can be obtained from phosphate rock slimes by sand grinding the aqueous slimes and then subjecting the slimes to negative ion froth flotation in an alkaline circuit in accordance with our invention. In the examples all mesh sizes refer to Tyler screen values. Reagent quantities are based on the dry weight of the slimes. Particle size values reported in the examples were determined by the sedimentation procedure described in a publication by F. H. Norton and S. Speil in J. Am. Ceramic Soc, 21: 89 (1938).

In accordance with this invention, a concentrate analyzing 74.80% BPL (principally apatite) was obtained at an 85.4% BPL recovery from 25.3% BPL slimes from a commercial phosphate rock washer plant in Montana (Silver Bow tailings).

The slime tailings at 24.4% solids were placed in a drum containing minus plus 35 mesh angular silica sand. The drum charge was as follows:

Wt. percent Sand 67 Slimes 8 Water 25 The drum, about half filled with the charge, was rotated about its horizontal axis at a peripheral speed of about 250 ft./min. for 17 hours. The sand was screened from the slimes and a particle size distribution curve of the slimes made before and after sand grinding with the following results:

Particle size distribution of phosphatic slimes 1 Equivalent spherical diameter. 2 Average equivalent spherical diameter=0.8 micron.

The ground slimes at 24.4% solids were diluted to 10% solids with soft water and deflocculated (dispersed) by agitating the slimes with 5 pounds per ton of 0 brand sodium silicate solution for 5 minutes. 0 brand sodium silicate contains about 8% Na O, 30% SiO and 62% E 0, weight basis. The slip was screened and to the minus 325 mesh fraction the following reagents were added in the order given.

Reagents: Pounds/ton of dry slimes NH OH 4 As aqueous emulsion- Crude tall oil fatty acids 10.7 Neutral calcium Petronate 10.7

Crude tall oil fatty acids 1.2

The neutral calcium Petronate had the following analysis:

Percent Calcium sulfonate complex 41.0 Sodium sulfonate Trace Mineral oil 58.5 Water 0.5

Percent Ca in sulfonate complex=2.85%.

Flotation beneficiaiion of sand ground phosphatic slimes Weight Percent Percent Product Percent BPL. BPL Dis tribution Feed 100. 0 25. 37 100. 0 Mach. Disch.1 30. 9 2.16 2. 7 Mach. Disch.-2 19. 4 3. 74 3.0 Mach. Diseh.3 11.1 5. 88 2. 7 Mach. Disch.4 5.0 10.10 2. 3 Mach. Disch.5 3. 2 17. 39 2. 3 Mach. Disch.6-. 1.6 25. 24 1.6 Froth Product 28. 2 74. 85. 4

These data show that over of the bone phosphate of lime content of the feed slimes was recovered in the form of a phosphate concentrate of 74.80% BPL grade.

The procedure was repeated with the sand grinding time reduced to 4 hours, producing a slime of the following particle size distribution (expressed as equivalent spherical diameters): 83% minus 9 microns, 76% minus 6 microns, 55% minus 2 microns, 50% minus l.5 microns and 24% minus 0.5 micron (average equivalent spherical diameter of 1.5 microns). The BPL grade and recovery of this process were substantially identical to the grade and recovery obtained with the longer grinding time.

A portion of the deflocculated minus 325 mesh Silver Bow tailings was floated without a preliminary grinding step and employing the same reagents and reagent quantities shown above with 1 rougher float and 3 cleanings. A 53% BPL grade concentrate was obtained with a 91% recovery by this procedure. This result was markedly inferior to the 74.80% BPL and 85.4% recovery of the process of the invention.

While our process has been described with especial reference to its application to the treatment of phosphatic slimes, it will be distinctly understood that it is fully within the scope of our invention to utilize our process, as described hereinabove with specific reference to phosphatic slimes, to renew the surface of other finely divided minerals, especially particles that are minus 10 micron equivalent spherical diameter, and contain a substantial amount of particles finer than /2 micron equivalent spherical diameter. When processing other slimed. ore pulps, the process, as described in connection with the processing of the phosphatic slimes, must be modified within the skill of the art to utilize suitable flotation reagents and conditions after the treatment with the finely divided grinding medium.

We claim:

1. A method for obtaining a phosphate concentrate from aqueous phosphatic slimes produced by the hydraulic washing of phosphate rock, said aqueous slimes consisting of particles substantially all of which are finer than 325 mesh, Tyler standard, and a major weight percent of which are finer than 9 microns, equivalent spherical diameter, Which comprises adding plus 325 mesh, Tyler standard, particles of a hard inert grinding medium into said aqueous slimes,

partially filling a horizontal drum with said aqueous slimes and added grinding medium and rotating said drum about its horizontal axis with said aqueous slimes and added grinding medium for at least about 10 minutes to produce a particle size reduction of said slimes at a speed such that the aqueous slimes and grinding medium is maintained substantially as a pool adjacent the lower portion of the drum and the individual particles of grinding medium are suspended within the aqueous slimes and travel in generally closed elliptical path therein,

separating said grinding medium from said aqeous slimes,

agitating said slimes with a fatty acid collector reagent and a hydrocarbon oil cooperative reagent so as to condition said slimes for froth flotation,

and subjecting said slimes thus conditioned to froth flotation in an alkaline circuit to obtain a froth product which is a concentrate of phosphate values originally in the slimes and a tailings.

2. The method of claim 1 wherein said plus 325 mesh particles of grinding medium are composed predominantly of particles finer than about 10 mesh and coarser than 35 mesh, Tyler standard.

3. The method of claim 1 wherein said added particles are composed of silica sand.

4. The method of claim 1 wherein said phosphate rock is Western phosphate rock.

5. A method for obtaining a phosphatic concentrate from aqueous phosphatic slimes produced by the hydraulic washing of Western phosphate rock, said aqueous slimes consisting of particles a major weight percentage of which is finer than 9 microns, equivalent spherical diameter, which comprises:

incorporating plus 325 mesh, Tyler standard, particles of silica sand into said aqueous slimes using a quantity of sand such that the total solids in the resulting mixture is within the range of about 70% to 80% and the slimes are at about 6% to 25% solids, rotating said slimes with sand in a horizontal drum in a manner such that said slimes are maintained substantially as a pool occupying only the lower portion of the drum and the individual particles of sand travel in continuous, generally elliptical paths within the slimes for a time sufiicient to reduce the size of solids originally in the slimes,

removing said sand from the slimes and recovering an aqueous slip of ground slimes,

incorporating sodium silicate dispersing agent into said aqueous slip of ground slimes,

agitating said aqueous slip with a fatty acid collector reagent and a hydrocarbon oil cooperative reagent so as to condition said slip for froth flotation,

and subjecting said slip thus conditioned to froth flotation in an alkaline circuit to obtain a froth product which is a concentrate of phosphate values originally in the slimes and a tailing.

6. A process for improving the selective flotation of slimed apatite from slimed clayey gangue in a minus 325 mesh, Tyler standard, aqueous ore pulp containing a substantial quantity of colloidal slimes which comprises incorporating plus 325 mesh, Tyler standard, hard inert grinding medium into said ore pulp and partially filling a horizontal baffie-free cylindrical drum having a smooth inner surface with said pulp and said grinding medium, rotating said drum about its horizontal axis at a speed such that said pulp within the drum is in the form of a pool occupying substantially only the lower portion of the.

drum and the individual particles of grinding medium travel in continuous generally elliptical .paths within the pulp continuing said rotation for at least 10 minutes to produce a particle size reduction of said ore pulp, separating said grinding medium from said pulp and subjecting said pulp to froth flotation in the presence of a collector reagent selective to said apatite.

7. The process of claim 6 wherein said aqueous ore pulp which is rotated with said grinding medium is an alkaline pulp containing sodium silicate as a dispersant.

References Cited by the Examiner UNITED STATES PATENTS 1,164,264 12/1915 Davidson 24130 1,585,756 5/1926 Borcherdt 2095 2,165,268 7/1939 Vogel-Jorgensen 209l66 2,991,017 7/1961 Hukki 24126 3,097,801 7/1963 Duke 24116 3,107,214 10/1963 Duke 209l66 HARRY B. THORNTON, Primary Examiner.

R. HALPER, Assistant Examiner. 

6. A PROCESS FOR IMPROVING THE SELECTIVE FLOTATION OF SLIMED APATITE FROM SLIMED CLAYEY GANGUE IN A MINUS 325 MESH, TYLER STANDARD, AQUEOUS ORE PULP CONTAINING A SUBSTANTIAL QUANTITY OF COLLOIDAL SLIMES WHICH COMPRISES INCORPORATING PLUS 325 MESH, TYLER STANDARD, HARD INERT GRINDING MEDIUM INTO SAID ORE PULP AND PARTIALLY FILLING A HORIZONTAL BAFFLE-FREE CYLINDRICAL DRUM HAVING A SMOOTH INNER SURFACE WITH SAID PULP AND SAID GRINDING MEDIUM, ROTATING SAID DRUM ABOUT ITS HORIZONTAL AXIS AT A SPEED SUCH THAT SAID PULP WITHIN THE DRUM IS IN THE FORM OF A POOL OCCUPYING SUBSTANTIALLY ONLY THE LOWER PORTION OF THE DRUM AND THE INDIVIDUAL PARTICLES OF GRINDING MEDIUM TRAVEL IN CONTINUOUS GENERALLY ELLIPITCAL PATHS WITHIN THE PULP CONTINUING SAID ROTATION FOR AT LEAST 10 MINUTES TO PRODUCE A PARTICLE SIZE REDUCTION OF SAID ORE PULP, SEPARATING SAID GRINDING MEDIUM FROM SAID PUPL AND SUBJECTING SAID PULP TO FROTH FLOTATION IN THE PRESENCE OF A COLLECTOR REAGENT SELECTIVE TO SAID APATITE. 